1. Field of the Invention
This invention relates to a crossed roller bearing having rollers interposed between an outer ring and an inner ring and a flange formed around the outer ring.
2. Description of the Related Art
For example, one of the conventional crossed roller bearings of the type described above is disclosed in JP-A-9-60647. For the conventional crossed roller bearing, an outer ring is cut into two ring parts, and then the two ring parts are joined with tie-bolts. The outer ring of the conventional bearing is divided into two parts in this manner for the purpose of arrangement of rollers between raceway grooves of the inner ring and the outer ring. For the arrangement of rollers between the raceway grooves, the inner ring is placed inside one of a pair of parts constituting the outer ring, then rollers are arranged between them, and then the other part is placed in such a manner as to put the top on the former part and is secured with tie-bolts.
Since the crossed roller bearing disclosed in JP-A-9-60647 as described above has the outer ring made up of two divided parts, the number of parts is disadvantageously increased. Further, since the two parts are joined with the tie-bolts, the number of man-hours is disadvantageously increased. When the two parts are joined with the tie-bolts, if a positioning error is caused in some degree, the rotation accuracy is reduced or the rotation torque is advantageously increased.
In order to solve the above problems, a crossed roller bearing having a one-piece type outer ring has been developed. This conventional crossed roller bearing is illustrated in FIGS. 5 and 6. The conventional crossed roller bearing has an outer ring 2 provided on the outer peripheral face of an inner ring 1. A raceway groove 3 is formed in the outer peripheral face of the inner ring 1 and a raceway groove 4 is formed in the inner peripheral face of the outer ring 2. A loading hole 5 is formed in the outer ring 2 for loading rollers 6 from the loading hole 5. The rollers 6 loaded from the loading hole 5 are arranged such that the axes of the adjacent rollers 6 are at right angles to each other. In order for the bearing to be capable of simultaneously receiving a moment load, a load in an axial direction and a load in a radial direction, the axes of the adjacent rollers 6 are arranged at right angles to each other.
A flange 7 is provided on the outer ring 2. As is seen from FIG. 6, the plane shape of the flange 7 is circular and mounting holes 8 are formed in the flange 7 at approximately regular intervals. Bolts (not shown) are fitted through the mounting holes 8 so as to secure the flange 7 to, for example, a housing (not shown).
As is clear from FIG. 5, the conventional bearing has a thickness in the axial direction resulting from addition of the thickness of the flange 7 to the thickness of the outer ring 2 in the axial direction. In other words, the flange 7 is positioned close to the outermost of the bearing and out of alignment with the position of the outer ends X of the raceway grooves 3 and 4 in the axial direction.
FIG. 5 shows a lid member 9 for covering the loading hole 5. A V-shaped groove 10 is formed in the lid member 9 and is connected to the raceway groove 4 of the outer ring 2 to form a part of the raceway groove 4. The lid member 9 covers the loading hole after all the rollers 6 are incorporated from the loading hole 5 as described above. Then, a pin 9a is fitted into a pin hole formed in the lid member 9 so that the lid member 9 is secured to the outer ring 2.
The conventional crossed roller bearing structured as described above has a great thickness as whole in the axial direction because the thickness of the flange 7 is added to the thickness of the outer ring 2 in the axial direction. The great thickness causes a disadvantageous increase in size and weight of the bearing. In particular, when the bearing is used, for example, for a joint portion of an industrial robot performing a precision task, an increase in size and/or weight of the bearing not only leads to an increase in size of the industrial robot, but also interferes with the precise and quick operation.